1. Field of the Invention
The present invention relates to an audio apparatus, and in particular, to an audio apparatus including a tuner unit and a digital reproducing unit.
2. Description of the Related Art
As a consumer-use audio apparatus, there is a so-called system stereo. This system stereo, for example, is comprised of an AM-FM tuner, recording/reproducing components such as a cassette tape recorder, a compact disc (CD) player, a mini disc (MD) recorder/player and the like, and they are integrated and housed in a single cabinet.
FIG. 6 is a frontal view showing one example of a specific appearance of such system stereo. This system stereo in this example can handle AM/FM broadcasts, a CD, a compact cassette as its source, and optionally an MD recorder/player unit is connected if desired.
This system stereo is formed generally into a rectangular shape, and on the front panel there are provided a display 11, a CD disc tray 12, and a cassette loading slot 13. Also, on the front panel there are provided a power on-off 25 key 14, function keys 15, a volume up-down key 16a, 16b, and operation mode control keys 17.
In this example, these keys 14 to 17 are composed of non-lock type push button switches. The function keys 15 are provided for switching over the sources, and by pushing this function key 15, either of the AM broadcast tuner, FM broadcast tuner, a CD player, a cassette player, or a MD recorder/player can be selected. Further, the operation mode control key 17 serves to shift a receiving frequency to receive a desired broadcast station when receiving AM or FM broadcast waves, as well as serves to switch a mode of operation between a reproducing mode, a pause mode, a stop mode, etc. when using the CD player or cassette recorder/player.
Further, on the left and the right sides of the system stereo, there are disposed a pair of speakers 28L and 28R for left and right channels, respectively. A system control of this system stereo is executed by a built-in microcomputer (not shown).
Therefore, according to this system stereo described above, advantages in space-saving, a reduced production cost, and the like can be achieved, and also eliminating the need of messy wiring around of cables between respective components.
However, this system stereo as described above has such a drawback that radio frequency noise components of a clock of the built-in microcomputer for use in the system control reaches an AM or FM frequency bands and interferes with the reception of the AM or FM broadcast waves.
Therefore, it is arranged in some of the system stereos such that while receiving broadcast waves, a clock frequency of the microcomputer is slightly shifted corresponding to the receiving frequency of the broadcast so as to ensure for the radio frequency noise components of the clock not to coincide with or come into the vicinity of the receiving broadcast frequency, thereby preventing the interference with the reception of broadcasting. Here, the Japanese Patent No. 3122102 is referred to as a related art.
Generally, a CD player or an MD recording/reproducing unit executes a digital processing of audio signals, and also various controls thereof is digitally processed. Therefore, radio frequency noise components which reaches AM or FM frequency bands are also generated in the CD player and MD recording/reproducing unit. In addition, in the system stereo as described above, the tuners of AM broadcast and FM broadcast as well as the CD player are disposed in the same cabinet.
Thereby, it often occurs that radio frequency noise components generated in the CD player readily enters the tuner thereby causing interference with the reception of broadcasting, in particular, the reception of AM broadcast waves. That is, in case of receiving broadcast waves from a local station, as a signal level of the received signal is substantially high, the radio frequency noise components of the CD player are suppressed by an automatic gain control (AGC), thereby causing no problem effectually. However, in case of receiving broadcast waves from a remote station or under a weak receiving condition, its reception is likely to be affected by the radio frequency noise components due to a weak signal level of the received signal.
In order to solve this problem as described above, the power of the CD player may simply be turned off when receiving the broadcast waves. That is, when listening to a radio broadcast station, as it is not required to reproduce a CD, there will be no problem even if the power of the CD player is turned off. If the power of the CD player is turned off, the CD player no more produces radio frequency noise components, thereby preventing for the CD player to interfere with the reception of the broadcast waves.
However, as for the CD player, when the power thereof is turned on, it needs to initialize each section and read out information from a table of contents (TOC), accordingly, it is required a few seconds to complete all of these initializing processing.
Thereby, if the power of the CD player is arranged to be turned off during the reception of the broadcast waves, and when the source of the system stereo is switched from the AM broadcast tuner to the reproduction of a CD, a non-operable state of the system stereo occurs for such few seconds.
Of course, if the power of the CD player is kept turned on during the time of listening to the broadcast station, a CD can be immediately reproduced as soon as the source is switched from the reception of the broadcast station to the reproduction of CD. However, in this case, the above-mention problem of interference with the reception of broadcast waves is involved. The present invention is contemplated to solve the above-mentioned problems associated with the related art.